In recent years, the use of the vehicle which equips with an idle stop and go (ISG) device is currently on the rise so as to satisfy a fuel efficiency enhancement demand. In the related art, a vehicle having an ISG device can be stopped by receiving information, for example, on a vehicle speed, a rotational speed of an engine, a cooling water temperature, a tip-in/tip-out of an acceleration pedal, an on/off of a brake penal, etc. The engine can be stopped if the engine maintains an idle state for a predetermined time period, thus enhancing fuel efficiency of the vehicle.
In case of such a vehicle which equips with the ISG device, the engine will start when a driver's start intention, for example, the operation of an acceleration pedal, etc. after the activation of the ISG device, is confirmed. In order to obtain start stability at the time of an engine start, it needs to carry out a synchronization control of the engine by accurately determining an angle of a crank when starting the engine.
FIG. 3 is a view illustrating a crankshaft angle detection device to measure a rotational angle of the crank. A sensor wheel 20 installed coaxial with a crankshaft 30 includes a plurality of teeth 21 on an outer circumference thereof. One or two teeth are missing from the teeth 21 so as to indicate a top dead point of the piston. A crankshaft angle sensor 10 is installed near the sensor wheel 20 so as to detect the presence of the teeth 21. The crankshaft angle sensor 10 is able to transmit a predetermined waveform signal, as illustrated in FIG. 2, by detecting the teeth which pass in front of the sensor during the rotation of the sensor wheel 20. Here, in the waveform, the time period from one falling edge to the next falling edge is called a tooth period (T). The rotational angle of the crankshaft 30 can be measured by analyzing the above-mentioned signal.
In case of the idle stop of the engine of the ISG device-mounted vehicle, an engine reverse rotation phenomenon may occur since the crankshaft fluctuates, for example, due to a friction, etc. between vehicle wheels and the ground before the engine completely stops (a stall). For this reason, in case of the ISG device-mounted vehicle, it is essential for the sake of a stable restart of the engine to accurately detect any reverse rotation and reverse rotation level of the engine at the time of the idle stop stage of the engine.
In order to determine any reverse rotation of the engine, according to the related art, information on a cam shape which can be measured using a tooth period measured by the crankshaft angle sensor or the information on a cam shape measured using a cam sensor.